Inter symbol interference (ISI) is a form of distortion of a signal in which one symbol interferes with subsequent symbols. ISI resulting from a communications channel can greatly reduce an eye opening at an input of a receiver. A decision feedback equalizer (DFE) has a number of taps that can be optimized to compensate for the ISI effects of a communications channel. It accomplishes this by approximating the pulse response of the channel.
Some applications contain multiple impedance discontinuities that may cause reflections to show up over a wide range of Unit Intervals (UIs). To compensate for this, a large number of taps may be needed, which may be impractical in certain situations (e.g., constraint by requirements such as power consumptions, space availabilities, costs or the like). Since the effects of reflections may not affect all taps, only some DFE taps may be utilized to selectively target where significant reflections may occur. Floating taps may be utilized for such purposes.
A floating tap is a tap whose tap value and position in time are adjustable. The time position of these floating taps must be located such that they line up in time with the reflections. Determining the optimal position is difficult unless test equipment is available that can accurately measure the reflection propagation times and provide the system designer with enough information to select the proper locations to apply these taps. The test system would need to be instrumented at the input to the receiver so that the reflection delays can be measured. This would have to be instrumented for every channel of every system that the designer wished to apply this feature. This makes it impractical for the system designer or end users. Therein lies a need for a system and method for optimizing floating decision feedback equalizer (DFE) receiver taps.